By existing methods, photopatterning of liquid phase polymerizations occurs using a photomask where a pattern is defined by the clear and dark regions. The initiating light penetrates through the clear region of the mask, exposes the underlying solution, and initiates the polymerization reaction. The dark regions block the initiating light and prevent the polymerization reaction. Patterned hydrogels have been fabricated using photopolymerization reactions in combination with a photomask to create 3-D structures. For example, photopatterning has been used to form patterned hydrogels from liquid phase polymerizations with thickness up to 180 micrometers and a resolution down to 25 micrometers (Beebe et al. (2000) Nature 404:588–90). Photopatterning has emerged as a simple, inexpensive technique that can be performed in standard laboratories to pattern channels for microfluidics (Khoury et al. (2002) Lab on a Chip 2:50–5) or cells in 3-D gels for tissue engineering (Snyder & Desai (2001) J. Biomater. Sci. Poly. Ed. 12:921–32; Liu & Bhatia (2002) Biomed. Microdev. 4:257–66; Koh et al. (2002) Langmuir 18:2459–62). However, the limitations of patterning from liquid phase solutions using photolithography techniques include limited pattern depth and resolution.
Recently, the fabrication of a well-defined porous material has been reported using indirect solid free-form fabrication (iSSF). This technique uses a computational design of a 3D structure that is printed layer-by-layer using specially designed printing equipment to form a 3D structure (e.g., that is made out of wax). A polymer solution (e.g., poly(lactic acid) containing salt as a poragen forming species) is then cast onto the 3D structure. Upon removing the wax and leaching out the salt, a porous scaffold with a well-defined macro-architecture is generated. This approach to patterning porous materials is expensive and requires specialized equipment.
Thus, there is a need for methods for photopatterning hydrogels and for making porous hydrogel scaffolds that overcome the disadvantages of prior art methods.